Electronic packages commonly employ various surface mount electronic devices assembled onto electrical circuitry on a printed circuit board. The printed circuit board generally includes a dielectric substrate (e.g., organic resin reinforced by fibers) and single or multiple layers of electrically conductive circuit traces. Many circuit boards include contact pads for solder connecting components to the electrical circuitry on the circuit board.
Some power electronic circuits require the use of silicon bare die components soldered directly to substrate materials. The choice of materials typically employed in these applications are generally limited by the need for high thermal performance properties and a coefficient of thermal expansion (CTE) closely matched to the silicon bare die components. Examples of some substrate materials include aluminium nitride (ALN), silicon nitride (SiN), or beryllium oxide (BeO). The circuit design flexibility using these substrate materials is generally limited and the materials are generally costly.
Due to the low cost and high conductivity of copper, it is generally desirable to attach the silicon bare die directly to a copper tab or to a copper pad on a circuit board substrate. However, because of the large coefficient of thermal expansion mismatch between the copper and the silicon die, the solder joint of a silicon die used in power electronics generally may not successfully survive thermal cycling. Solder joint failures may result during temperature excursions encountered during normal operating cycles, particularly when used in the automotive environment. The large temperature fluctuations in the electronic package experienced with continuous power cycles generally produces fatigue in the solder joints. This cyclical thermal fatigue may result in sheer stress fatigue of the solder joint, especially when combined with vibrations.
It is therefore desirable to provide for an electronic package having a die to copper substrate connection that is less susceptible to thermal fatigue. In particular, it is desirable to provide for an electrical connection that allows the use of high powered die components to be soldered onto a copper circuit on a substrate, in a manner that is less susceptible to adverse affects caused by variations in the thermal coefficient of expansion of the interconnecting materials.